(1) Field of the Invention
The present invention relates to a multilayer container and a method for producing the multilayer container, an easily-openable packaging container packaged by using the multilayer container, a method for packaging an article by using the multilayer container, and an apparatus for packaging an article (e.g. foods and drinks). More precisely, the present invention relates to a multilayer container suitable for heat sterilization packaging, which makes the setting of the heat sealing condition at heat sealing of a lid member easy. This invention is able to make a package which has not only an excellent sealing property but also easy openability and which can be opened with a stable opening force, a method and an apparatus for easily producing the multilayer container, an easily-openable packaging container packaged by using the above-mentioned multilayer container which provides a peeled surface having a good appearance and has an excellent resistance to boiling and retort treatment, a method for packaging, and an apparatus for packaging easily.
(2) Description of the Prior Art
Heretofore, flanged containers have been largely used for packaging foodstuffs or the like, and the container is sealed by heat sealing a lid member thereto after a content is filled therein. The heat seal container thus formed, however, is defective in that, if the sealing property is improved by increasing the heat seal strength, the openability at the time when the content is used is aggravated, resulting in the necessity for opening operation using an edged tool or the like, and, on the other hand, if a material having a proper interlaminer strength is selected to improve the openability, since the sealing property varies broadly depending on the heat seal conditions, such as temperature, pressure, and time, or owing to matters such as the content sandwiched between the heat seal surfaces, a uniform interlaminer strength cannot be obtained resulting in a decreased sealing property. Therefore, it cannot be used for a package in which the internal pressure is increased by heat sterilization such as boiling and retort treatment.
However, the traditional notion for the easy openability was limited to the openability in a peeling opening from the sealing area where a lid member and the flange portion of a container were heat sealed. Therefore, it has been proposed to decrease the heat seal property of the heat sealing layers. However, in this method, a good heat sealing property and an easy openability are incompatible and the appearance of the peeled surface is deteriorated (e.g. nap or thread) resulting in a decreased commercial value. Therefore, it cannot bring a substantial solution.
Heretofore, as the apparatus for forming a notch in the flange portion of a container, there is known an apparatus for forming a score for vending-cut in one lower portion of the flange portion of a container in order to improve the openability of a lid member (c.f. Japanese Utility Model Publication No. 48102/1983). The apparatus is composed of a heat blade capable of ascent and descent for forming a notch on the underside of a flange portion and a cooling bed for supporting the flange portion.
However, though such an apparatus can form a notch for cutting a flange along a straight line on a portion of the flange portion, accuracy of the depth or location of the notch is not always required of the apparatus according to the object of the apparatus, and, therefore, it is not satisfactory in the accuracy of the notch.